IBBE-SGX: Cryptographic Group Access Control using Trusted Execution Environments

While many cloud storage systems allow users to protect their data by making use of encryption, only few support collaborative editing on that data. A major challenge for enabling such collaboration is the need to enforce cryptographic access control policies in a secure and efficient manner.

Threat Model

Group Members are Trusted

Revoked Members are Malicious

Cloud Storage is Honest-but-curious

Collusion

NEW : Administrator is Honest-but-curious

We introduce IBBE-SGX, a new cryptographic access control extension that is efficient both in terms of computation and storage even when processing large and dynamic workloads of membership operations, while at the same time offering zero knowledge guarantees. IBBE-SGX builds upon Identity-Based Broadcasting Encryp-tion (IBBE). We address IBBE's impracticality for cloud deployments by exploiting Intel Software Guard Extensions (SGX) to derive cuts in the computational complexity.

Moreover, we propose a group partitioning mechanism such that the computational cost of membership update is bound to a fixed constant partition size rather than the size of the whole group. We have implemented and evaluated our new access control extension. Results highlight that IBBE-SGX performs membership changes 1.2 orders of magnitude faster than the traditional approach of Hybrid Encryption (HE), producing group metadata that are 6 orders of magnitude smaller than HE, while at the same time offering zero knowledge guarantees.

The research leading to these results has received funding from the French Directorate General of Armaments (DGA) under contract RAPID-172906010. The work was also supported by European Commission, Information and Communication Technologies, H2020-ICT-2015 under grant agreement number 690111 (SecureCloud project) and partially supported by the CHIST-ERA ”DIONASYS” project.